Environmental filtering and biotic interactions act on different facets of the diversity of benthic assemblages associated with eelgrass

Disentangling the effect of space, time, and environmental and anthropogenic drivers on coastal macrobenthic β diversity in contrasting habitats over 15 years

Coastal zones are biodiversity hotspots and deliver essential ecosystem functions and services, yet they are exposed to multiple and interacting anthropogenic and environmental constraints. The individual and cumulative effects of these constraints on benthic communities, a key component of coastal ecosystems, and their variability across space and time, remains to be thoroughly quantified to guide conservation actions. Here, we explored how the presence of biogenic habitats influences the response of benthic communities to natural and anthropogenic constraints. We investigated this effect in both intertidal and subtidal habitats exposed to different pressures. We used data collected in the North-East Atlantic over 15 years (2005-2019) as part of the REBENT monitoring program, covering 38 sites of bare sediments, intertidal seagrass beds and maerl beds. We collected a range of environmental variables and proxies of anthropogenic pressures and used variation and hierarchical partitioning with redundancy analyses to estimate their relative effect on macrobenthic communities. We used descriptors modeling spatial and temporal structures (dbMEMs) to explore the scale of their effects and potential missing predictors. The selected variables explained between 53 % and 64 % of macrobenthic β diversity depending on habitat and depth. Fishing pressures, sedimentary and hydrodynamics variables stood out as the most important predictors across all habitats while proxies of anthropogenic pressures were overall more important in intertidal habitats. In the intertidal, presence of biogenic habitat strongly modulated the amount of explained variance and the identity of the selected variable. Across both tidal levels, analysis of models' residuals further indicated that biogenic habitats might mitigate the effect of extreme environmental events. Our study provides a hierarchy of the most important drivers of benthic communities across different habitats and tidal levels, emphasizing the prominence of anthropogenic pressures on intertidal communities and the role of biogenic habitats in mitigating environmental changes.

Microscale dispersion of intertidal seagrass macrofauna

Previous studies of dispersion of intertidal seagrass-associated macrobenthos in subtropical Moreton Bay, Queensland, showed that patchiness characterised its assemblage abundance with scale-invariant magnitude across areas ranging from >8000 to 0.1 m2. Those studies were here continued across the smaller scales (down to 0.014 m2) arguably more relevant to the dominant 2-10 mm long animals, using 16 replicate blocks of 5x5 contiguous 0.0024 m2 cores nested within the previously studied site. At microscales ≥0.09 m2, the earlier congruence of conclusions derived from patchiness indices and spatial autocorrelation broke down. At >0.014 m2, adjacent points (cores) no longer together formed larger spatial units of related abundance (i.e. showed no autocorrelation), but point abundances were still highly disparate (as reflected in patchiness indices). Congruent indications of patchiness only manifested at 0.014 m2 spatial scales. Assemblage dispersion pattern was partly consequent on one microgastropod (Pseudoliotia) occurring superabundantly in scattered 0.0024 m2 hotspots.